A conventional armrest structure is shown in FIGS. 13 to 16 and generally includes a armrest case 81 with a fixing device 82 at the underside thereof and the fixing device 82 has a rack portion 821 on a side thereof and a ridge 822 is located at the underside thereof so that the rail 83 of the armrest case 81 is allowed to move upward. A fixing plate 84 includes a tooted portion 841 on each of two sides thereof and fixing posts 842 are located at the underside thereof so as to be accommodated in the hole 823 of the fixing device 82 and respectively fixed to the armrest (not shown). Two gears 85 are respectively located on two sides of the fixing device 82 and the teeth 851 are engaged with the toothed portion 841 of the fixing plate 84. An adjustment member 86 has a first toothed portion 861 which is engaged with the teeth 851 of the gears 85, and the second toothed portion 862 is engaged with the rack portion 821 of the fixing device 82. The spring 863 of the adjustment member 86 is located between the controlling portion 864 and the stop 811 of the case 81. When adjusting the armrest back and forth, the adjustment member 86 is pressed to compress the spring 863 so that the first toothed portion 861 is separated from the teeth 851, and the second toothed portion 862 is separated from the rack portion 821 as shown in FIG. 14. The user holds the case 81 and moves the rail 83 of the case 81 along the ridge 822 of the fixing device 82 so that the case 81 can be moved back and forth. When the case 81 is moved to a desired position, the adjustment member 86 is released and the spring 863 moves the adjustment member 86 back to its original position. The first toothed portion 861 of the adjustment member 86 is engaged with the teeth 851 of the gear 85, and the second toothed portion 862 is engaged with the rack portion 821 of the fixing device 82 to position the case 81 as shown in FIG. 15.
When adjusting the case 81 left and right, the adjustment member 86 is pressed to compress the spring 863 so that the first toothed portion 861 is separated from the teeth 851, and the second toothed portion 862 is separated from the rack portion 821. The user holds the case 81 and moves hole 823 relative to the fixing posts 842 of the fixing member 84, and the teeth 851 is rotatable relative to the toothed portion 841 of the fixing plate 84 to swing the case 81. When the case 81 is moved to a desired position, the adjustment member 86 is released and the spring 863 moves the adjustment member 86 back to its original position. The way that the adjustment member 86 moves is the same as the previous mentioned way to position the case 81 as shown in FIG. 16.
As shown in FIGS. 17 and 18, the pivotal portion 92 of the pivotal frame 91 is connected to the chair and the engaging portion 93 of the pivotal frame 91 has multiple slots 94 located in the hollow movable case 95 which includes multiple positioning recesses 96 in the top of inside thereof. The pivotal shaft 971 of the engaging rod 97 is engaged with the positioning recesses 96. The engaging rod 97 has a hook 972 at the bottom thereof and an operation portion 973 is formed on the top of the engaging rod 97. When adjusting the height of the armrest, the user pivots the operation portion 973 located outside of the movable case 95, the engaging rod 97 is pivoted about the pivotal shaft 971 to shift the hook 972 away from the slot 94 of the pivotal frame 91, so that the movable case 95 can be moved upward and downward. When the user releases the operation portion 973 of the engaging rod 97, the hook 972 swings due to the weight of the engaging rod 97 and hooks the slot 94 to position the armrest.
When the armrest is adjusted in horizontal direction, the fixing plate extends through the hole of the fixing device and is fixed to the pivotal arm on the armrest so as to form a pivotal point. The adjustment member is disengaged from the gears and the fixing device, the frame moves relative to the ridge of the fixing device so that the case can be moved back and forth. However, when the armrest is moved left and right, the action has to be proceed after the action for adjusting the armrest back and forth, or the action for adjusting the armrest left and right uses the hole relative to the fixing posts of the fixing device, and the teeth of the gears pivotal relative to the toothed portion of the fixing member. Once the armrest is positioned, the first toothed portion of the adjustment member is engaged with the teeth of the gears, and the second toothed portion is engaged with the toothed portion of the fixing device. Accordingly, the adjustment and positioning of the armrest is mainly relied on the distance between the teeth of the gears to adjust the gears so as to set the horizontal distance, and the engagement of the gears and the related parts. If the teeth are narrow and thin, then the adjustment can be made more precisely, but the teeth are easily broken. On the contrary, if the teeth are wide and thick, the adjustment can only be made at larger scale and the teeth are more strong and durable. The precise and fine teeth of the gears require the toothed portion of the fixing device and the toothed portion of the fixing member to be precise and fine, and this means higher manufacturing cost is needed.
Besides, for the height adjustment, the engaging rod is pivoted relative to the pivotal shaft to let the hook to be hooked to the slots of the pivotal frame. However, the engaging rod easily contacts the operation portion unintentionally to disengage the hook from the slot to affect the adjustment of the height of the armrest. This is a problem to be improved.
The present invention intends to provide an armrest structure which improves the shortcomings of the conventional armrests.